This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. To date, approximately 500-600 cases of vertical transmission of human immunodeficiency virus type 1 (HIV) occur annually in the United States. The dramatic reduction in vertical transmission rates in the United States is related to several factors, including: increased provision and acceptance of voluntary counseling and HIV testing of pregnant women, improvements in the medical management of HIV- infected pregnant women, and the development and increased acceptance of interventions to decrease the risk of mother-to-child transmission of HIV. Specific U.S public Health Service guidelines recommend antiretroviral therapy (ART) during pregnancy appropriate to maximize health of the women. However, data regarding the effectiveness and safety of and adherence to ART during pregnancy are limited. In addition, important questions remain unanswered regarding risk factors for vertical transmission and why interventions fail. and the safety of interventions for women and their infants.